The hot gases issuing from an incinerator are typically cooled and scrubbed in a scrubbing tower. The solution produced in this tower as a result of the scrubbing liquid picking up impurities from the gas is clarified with the decantate being recycled for use as the scrubbing liquid and the sludge being disposed of.
Such a system has the considerable disadvantage that when a synthetic resin such as polyvinyl chloride is burned destructive elements or compounds, such as hydrochloric acid, are present in the incinerator gas. The recirculation of the scrubbing liquid after clarification by means of sedimentation or similar thickening is ineffective in such an arrangement in the long run, as it merely serves to concentrate the acidity of the scrubbing liquid. It is therefore impossible to dispose of this scrubbing liquid in a conventional manner due to its toxicity. Neutralization of the scrubbing liquid prior to disposal of it is similarly ineffective as the neutralizing agent only creates soluble neutralization products which are similarly highly polluting.
Another principal cause of the presence of noxious elements and substances in incinerator gas is inadequate combustion in the incinerator due to fluctuating gas pressure. As a rule a pump or blower is provided downstream of the incinerator in a conduit connected to this incinerator. The operation speed, and therefore the gas displacement or throughput of this blower, is varied in accordance with the type and quantity of the refuse being burned. This presents little difficulty, however other problems are created with this fluctuating pressure in the downstream scrubbing tower which is only efficient in a relatively limited pressure range. Thus the scrubbing tower will operate at a relatively low efficiency level occasionally, causing considerable pollution. This cannot be permitted so it is necessary carefully to control the type and quantity of garbage loaded into the incinerator so as not to exceed the operating range of the scrubbing tower.